The present invention relates to a single-sideband generator.
Single-sideband generation is a well known technique for transmitting as many channels as possible on the limited bandwidth of a transmission system. One known method is to use a balanced modulator which modulates a carrier with a modulating signal to produce a carrier-suppressed both-sideband signal which is filtered through a complex band-pass filter to obtain a single-sideband signal. Another typical method for single-sideband generation is to employ two 90-degree phase shifters for respectively delaying the phase of a modulating signal and a carrier by 90 degrees each. The delayed modulating signal and carrier are respectively applied to the inputs of a first balanced modulator. The original modulating signal and carrier, both advanced by 90 degrees from the outputs of the phase shifters, are applied respectively to the inputs of a second balanced modulator. The outputs of the modulators are combined in an adder to produce a single sideband signal which is filtered through a low-pass filter to eliminate the high-frequency component.
For a monolithic integrated circuit chip it is important to reduce the number of pin terminals for connection to outside circuitry in order to reduce the cost of the chip. To design a monolithic integrated circuit chip for a single-sideband generator, a number of capacitors employed in the generator must be located outside the chip and connected through pin terminals. The pin terminals thus increase with the number of capacitors employed in the single-sideband generator. The above-mentioned prior art single-sideband generators are not satisfactory in terms of the number of capacitors.